This invention relates to a duct type air conditioning apparatus which has adopted a variable air quantity control system capable of regulating temperature in each room independently of the other.
The central air-conditioning system of a type which carries out air-conditioning by distribution of temperature-regulated air to every room through air ducts possesses various meritorious effects in comparison with the conventional heat pump chiller/fan coil system, the package air-conditioners decentralized arrangement system, and others in that it can easily incorporate therein various facilities like a humidifier, a high performance air filter for cleaning external air introduced into the system, and a total heat-exchanger, hence it is able to perform a high grade air conditioning operation, it has the least losses in its heat transporting system, and yet it can utilize the room space with high effectiveness because the room to be air-conditioned has only an outlet port for the conditioned air, and an inlet port for the exterior air to be introduced into the room. Therefore, such centralized air-conditioning system has so far been used widely for the air-conditioning of a large-sized building. Of various centralized air-conditioning systems, the variable air quantity control system adapted to the energy-saving operations (hereinafter simply called "VAV system") is capable of controlling temperature in a plurality of rooms, each having different heat load, independently of the other, is capable of stopping the air-conditioning operation in those rooms which are not in use, is also able to reduce the running cost of the air-conditioning system by changing the power for the air blower in accordance with quantity of air to be blown out, and, at the same time, is able to decrease the capacity of the heat source apparatus by taking into consideration of the rate of its use.
There are two types of the VAV system depending on the construction of the air quantity adjusting damper. The one is a system which uses a bypass type VAV unit (damper unit), wherein a ratio between the air quantity to be blown out into the room depending on the heat load of the room and the air quantity to be directly returned (or bypassed) to the heat source apparatus is adjusted. This type of the VAV system is used in most cases for the air-conditioning system utilizing the package air-conditioners which are difficult to control the capacity of its heat source apparatus, because of the air blowing quantity being kept constant, but this system has no energy-saving effect to be attained by control of the air blower.
The other is a type which uses a throttle type VAV unit, wherein the quantity of air to be blown out into the room is adjusted to an arbitrary value in accordance with the heat load of the room.
This VAV system detects a pressure in the air duct, which varies in conformity with the degree of opening of the damper, and controls the capacity of the air blower in a manner to bring this detected pressure value to a certain determined value. Therefore, when the heat load in the room decreases (that is to say, the air quantity becomes reduced, and the temperature of the air within the duct, at this time, is regulated at a constant level), the required performance of the heat source apparatus becomes reduced and the power for the air blower is also decreased.
As conventional techniques adopting the throttle type VAV unit, there are known that as in Japanese Unexamined Patent publication No. 196029/1982 and that as shown in FIG. 2.10(a) in Manual of Refrigeration and Air-conditioning (new fourth edition, technique for application) published by Nippon Reito Kyokai.
FIG. 1 of the accompanying drawing illustrates a schematic construction of an air conditioning apparatus to be the basis for explanation of the known art as well as the present invention. In FIG. 1, a reference numeral 1 designates rooms to be air-conditioned (in the illustrated case, three rooms are to be air-conditioned). A numeral 2 refers to a room unit disposed in the ceiling part of the building, and which is constructed with an air-filter 3, a heat exchanger 4 and an air blower 5.
A main air duct 6 is connected to the air outlet port of the room unit 2, and three branch ducts 7 are diverged from the main air duct 6. A throttle type VAV unit 8 is placed in each of the branch ducts 7. A damper 9 is rotatably fitted within each of the VAV units 8. An outlet port 10 is provided at the end part branch duct 7. An inlet port 11 is provided at the lower part of a door for each room 1, and an inlet port 12 is formed in the ceiling board above the corridor. An inlet duct 13 connects the inlet port of the ceiling to the air inlet port of the room unit 2.
A pressure detector 15 provided with a detecting part is placed in the air duct 6. Also, a temperature detector 16 is placed in the air duct 6.
A reference numeral 14 designates a room thermostat attached in each of the rooms, and a numeral 17 designates a heat source apparatus such as a heat pump connected to the heat exchanger 4.
In the conventional air conditioning apparatus, the degree of opening of the damper 9 is adjusted at an arbitrary position for each room in accordance with a difference between an established temperature set by a user in each room through the room thermostat 14 and an actual temperature of the air detected by a temperature detector. On account of this, the pressure in the air duct 6 changes depending on the degree of opening of the damper 9, the change of which is detected by the pressure detector 15, thereby varying the capacity of the air blower 5 so that the pressure in the air duct 6 becomes a predetermined pressure.
Since the temperature of the outlet air from the heat exchanger 4 varies with changes in the air blowing quantity, this temperature is detected by the temperature detector 16, on the basis of which the capacity of the heat source apparatus 17 is controlled to keep the temperature of the air at a predetermined temperature level.
The air is blown through the outlet port 10 into each of the room 1 at flow rates corresponding to the value of the heat load of the room. After air-conditioning, the air in the rooms 1 flows through the inlet port 11, corridor, the inlet port 12 formed in the ceiling and the inlet duct 13 to be returned to the room unit 2.
FIG. 2 is a diagram showing a relation of a cooling load to the quantity of air passed through the VAV unit as shown in FIG. 2.14 in the Manual of Refrigeration and Air-conditioning.
FIG. 2 shows that control is made such that when the cooling load is reduced to a certain value or lower, the quantity of air to be supplied becomes constant, and the temperature of the air becomes high as the cooling load reduces. This system is called a constant air quantity control system (CAV system) in which when a load changes, the temperature of air to be supplied is changed while the quantity of the air is maintained to the minimum extent. The system is suitably used for buildings in which air-conditioning operation is performed while the minimum quantity of ventilation of air is maintained. In FIG. 2, the abscissa represents a cooling load and the ordinate represents the quantity of air and the temperature of the air. In the Figure, the cooling load can be replaced by a difference between room temperature at present and an established temperature, and the quantity of the air can be replaced by the degree of opening of the damper 9. When a room-cooling operation is carried out, the temperature of each of the rooms decreases and the difference between the actual room temperature and the established room temperature becomes small. Accordingly, the dampers 9 are gradually closed whereby the quantity of air is balanced with the heat.
A relation of the quantity of air to a warming load is similar to that of the cooling load.
As other conventional techniques, there have been known those as disclosed in Japanese Examined Patent Publication No. 14979/1980, Japanese Examined Patent Publication No. 44853/1980, Japanese Examined Patent Publication No. 44854/1980 and Japanese Examined Patent Publication No. 24022/1980.
These techniques employ the VAV system in which the degree of opening of the damper 9 is adjusted by manual operation and the air blower and the heat source apparatus are controlled automatically. Namely, a single room temperature detector is placed in a room which tends to be frequently used among many rooms or a passage way of air to be returned. When the room temperature in that room decreases during room-warming operation, the quantity of the air is increased by increasing a pressure of air to be supplied. On the other hand, the quantity of the air is decreased by lowering the pressure of air when the room temperature is increased (This is referred to as a variable static pressure control method.). As another method, the temperature of air to be supplied is changed depending on the outer temperature, and the capacity of the heat source apparatus is controlled depending on a heat load (This is referred to as a variable temperature control method.).
Japanese Examined Utility Model Publication No. 35694/1981 discloses another VAV system in which the degree of opening of the damper is manually operated, and the air blower and the heat source apparatus are controlled automatically. This system is provided with a static air pressure control part, an air temperature control part and a timer device wherein at least one of the air blower and the heat source apparatus is operated with its maximum power for a certain time just after initiation of operation so that room temperature reaches an established room temperature as fast as possible when the air conditioning apparatus is started. In the conventional air conditioning apparatus using a throttle type VAV unit, the quantity of air is automatically controlled by the damper 9 in the VAV unit 8 in conformity with the heat load of each of the rooms without necessity of correctly balancing the quantity of air to each of the rooms by adjusting the sizes of the branch ducts 7 and the outlet ports 10 even when the heat load of each of the rooms is greatly different from each other. However, the heat load is much influenced by the outer temperature and heat produced in any room. Accordingly, when the heat load is large, and the temperature of air to be supplied and the pressure of air in the duct are controlled at a constant rate, the quantity of air becomes short even though the damper 9 is entirely opened and the room temperature of a room does not reach the established value. On the other hand, when the heat load is small, the quantity of air should be reduced by throttling each of the dampers 9, so that operation has to be performed under the condition that pressure loss is large.
In an air conditioning apparatus in which the dampers 9 are manually operated, when the quantity of air is adjusted by changing air pressure according to a temperature detected by the room temperature detector placed in the specified room, heat to be supplied to the other room having a different heat load is not balanced with heat loss of the room thereby causing change in room temperature. In this case, an occupant has to change by manual operation the degree of opening of the damper 9 of the room. Even in the case that the room temperature detector is placed in a passage of air to be returned, the same condition takes place. Namely, when the outer temperature changes, the heat load of each of the rooms does not constantly change because of heat to be produced in each of the rooms, and the pressure of air is changed only by the temperature of the returned air. Under the condition, when the quantity of air to be supplied to each of the rooms is changed, a caloric balance is lost and change of opening of the damper 9 is needed for some of the rooms.
When the room temperature detector is placed in a specified room which is frequently used, the room does not always produce the greatest heat load. Accordingly, when the air pressure is determined in accordance with the temperature of the room, there happens that it is insufficient to warm a room even though the damper 9 is entirely opened. When the damper 9 is closed for each of the rooms and the temperature of the specified room is not utilized, a suitable control for air pressure can not be obtained.
In addition, the heat load of each of the rooms is largely affected by heat produced in the rooms even though the temperature of air to be supplied is changed depending on the outer temperature and capacity of room-warming is adjusted. Accordingly, the optimum operation in conformity with the heat load can not be always obtained. Further, it is difficult to maintain the temperature of each of the rooms at a desirable level because the quantity of air to be supplied to each of the rooms having different heat load has to be adjusted by manually operable dampers 9.